Semiconductor substrate with stacked oxide and SOI layers with a molten or epitaxial layer formed on an edge of the stacked layers

ABSTRACT

A semiconductor substrate that prevents formation of particles from an edge part of the substrate. The substrate contains an on-substrate oxide film and an SOI layer stacked on the oxide film. A molten layer is formed on the edge part of the on-substrate oxide film and the SOI layer by mixing the SOI layer and the on-substrate oxide film to cover the edge part. An epitaxial layer may also be formed on the edge part of the on-substrate oxide film and the SOI layer to cover the edge part.

This application is a divisional of application Ser. No. 09/770,388,filed Jan. 29, 2001, now U.S. Pat. No. 6,563,172, which is itself adivisional of application Ser. No. 09/113,155, filed Jul. 10, 1998, nowU.S. Pat. No. 6,232,201. This application claims priority under 35U.S.C. §119(a)-(d) to Japanese Patent Application No. 10-4980, filedJan. 13, 1998. The contents of applications 09/113,155 and 09/770,388,and Japanese Patent Application No. 10-4980 are herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods for processing semiconductorsubstrates and the semiconductor substrates, and particularly to asemiconductor substrate processing method and a semiconductor substratein which formation of dust particles from the edge part of the substrateis prevented.

2. Description of the Background Art

While SOI (Silicon On Insulator) devices in which semiconductor elementsare formed on SOI substrates are superior to bulk devices in theirreduced junction capacitance and improved element isolation breakdownvoltage, the SOI devices have their unique problems as described below.

FIG. 32 shows a partial cross-section of an SOI substrate 10. The SOIsubstrate 10 includes a buried oxide film 2 and a single-crystal siliconlayer (hereinafter referred to as an SOI layer) 1 sequentially stackedin the upper main surface of a single-crystal silicon substrate 3.

SOI substrate manufacturing methods include an SIMOX (Separation byImplanted Oxygen) method and a bonding method, for example. The SOIsubstrate 10 shown in FIG. 32 is manufactured by the SIMOX method.

In the SIMOX method, an SOI structure is obtained by implanting oxygenions into a single-crystal silicon substrate to doses of 1×10¹⁸ to2×10¹⁸/cm² at 150 to 200 KeV and then annealing it at about 1300 to1400° C., for example.

FIG. 32 shows the edge part of the SOI substrate 10 in detail. In thefollowing description, a semiconductor substrate is referred toseparately in its upper main surface (the side on which semiconductorelements are formed), center part thereof (the part including the activeregion), edge part including the peripheral part around the center partand the side part, and lower main surface.

As shown in FIG. 32, the edge part is curved with a large curvature.Accordingly, when oxygen ions are implanted there from the verticaldirection, the oxygen ions are obliquely implanted, so that theeffective implantation energy is reduced. As a result, the buried oxidefilm 2 and the SOI layer 1 are thinner in the edge part. Further, thesurface of the edge part is not smooth but rough with irregularities.This phenomenon is general with silicon substrates formed by CZ(Czochralski) method. In the irregular part, the SOI layer 1 may be sothin that the buried oxide film 2 is exposed. In this condition, the SOIlayer 1 is prone to exfoliation.

In addition, the film-thinning process for the SOI layer 1 performed inthe SOI device manufacturing process facilitates the exfoliation of theSOI layer 1. The film-thinning process for the SOI layer 1 will now bedescribed.

The SOI layer 1 in the SOI substrate 10 is formed to an approximatethickness at the time of production of the substrate. The film-thinningprocess for the SOI layer 1 is performed to appropriately reduce thethickness of the SOI layer 1 according to specifications of desiredsemiconductor devices. In this process, the thickness of the SOI layer 1is adjusted by oxidizing the SOI layer 1.

The thickness of an oxide film formed on the SOI layer is generallydetermined on the basis of the thickness of the SOI layer 1 in thecenter part of the SOI substrate 10, or in the semiconductor elementformation region (active region). In this process, the thin SOI layer 1in the edge part of the SOI substrate 10 presents the problem as statedabove. The buried oxide film 2 may be exposed in some parts.

FIG. 33 is a schematic diagram showing the region X in FIG. 32. As shownin FIG. 33, the buried oxide film 2 is also irregular in the edge partof the SOI substrate 10, reflecting the shape of the irregular part DPof the SOI layer 1. Since oxygen ions are implanted from the verticaldirection, the irregularities on the SOI layer 1 and the irregularitieson the buried oxide film 2 are formed in shifted positions, which maycause the buried oxide film 2 to be exposed.

Next, FIG. 34 shows the SOI layer 1 and an oxide film OX formed thereonto thin the SOI layer 1. As the formation of the oxide film OX thins theSOI layer 1, the oxide film OX may be coupled to the buried oxide film 2or the SOI layer 1 may be completely oxidized in the edge part. In sucha case, the SOI layer 1 may be partially surrounded by the buried oxidefilm 2 and the oxide film OX. For example, the part 1A of the SOI layershown in FIG. 34 is surrounded by the oxide film OX and the buried oxidefilm 2.

When the SOI substrate 10 is wet-etched in this condition with anetching solution, such as hydrofluoric acid (HF), to remove the oxidefilm OX, the buried oxide film 2 will be etched away together with theoxide film OX, as shown in FIG. 35. Then, the SOI layer 1A will belifted off to be a particle, which will be suspended in the etchingsolution and may adhere to the center part of the SOI substrate 10. Ifparticles adhere to the semiconductor element formation region, it willcause defective formation of semiconductor elements to reduce theproduction yield.

In some cases, a polysilicon layer may be formed on the edge part andthe lower main surface of the silicon substrate 3 for gettering ofcontaminants like heavy metals taken in the wafer manufacturing processor in the wafer process for transistors. In this case, the SOI layer 1and the buried oxide layer 2 become uneven due to polycrystallinity ofthe polysilicon layer, and the SOI layer 1 will then partially come offto be particles, similarly to the phenomenon described above.

Particles may be produced also with SOI substrates formed by a bondingmethod (bonded substrates).

With a bonded substrate, the SOI structure is obtained by forming anoxide film on the upper main surface (on the main surface on whichsemiconductor elements are formed) of a silicon substrate 3, bondinganother silicon substrate thereon, and polishing that silicon substrateto a desired thickness. FIG. 36 shows a cross-section of the edge partof an SOI substrate 20 formed this way.

In FIG. 36, an on-substrate oxide film 6 and a silicon layer 7 areplaced on top of the other on the upper main surface of the siliconsubstrate 3 to form an SOI structure. The on-substrate oxide film 6corresponds to the buried oxide film and the silicon layer 7 to the SOIlayer.

With the SOI substrate 20 having this structure, the on-substrate oxidefilm 6 is exposed in the edge part. Hence, etching solution used inwet-etching may invade the exposed part to partially remove theon-substrate oxide film 6, causing the silicon layer 7 to be partiallyhung as shown in FIG. 37. In this condition, the silicon layer 7 isprone to come off to be a particle.

When the edge part of the on-substrate oxide film 6 and the siliconlayer 7 is imperfectly beveled, the periphery will show continuousirregularities in a plane view. The irregular part may come off intransportation of the substrate to produce particles.

As described above, conventional semiconductor substrates, particularlySOI substrates produced by the SIMOX method have the problem that theSOI layers in the edge part of the substrates may come off to beparticles, to reduce the production yield. Particles may be producedalso with SOI substrates manufactured by the bonding method.

SUMMARY OF THE INVENTION

A first aspect of the present invention is directed to a method forprocessing a semiconductor substrate having a first main surface, asecond main surface on the opposite side, and a side part, wherein apart where an active region is formed in the first main surface isdefined as a center part, and a part including a peripheral regionaround the center part in the first main surface and the side part isdefined as an edge part. According to the present invention, thesemiconductor substrate is an SOI substrate formed by an SIMOX method,and the semiconductor substrate comprises a buried oxide film and an SOIlayer formed in the first main surface in a sequentially stacked form,the method comprising a silicon-ion implantation step wherein siliconions are implanted into the edge part to eliminate the buried oxide filmformed in the edge part.

Preferably, according to a second aspect of the present invention, inthe semiconductor substrate processing method, the silicon ionimplantation step comprises the step of implanting the silicon ions fromthe side of the edge part in a direction of a radius of the SOIsubstrate.

Preferably, according to a third aspect of the present invention, in thesemiconductor substrate processing method, the silicon ion implantationstep comprises the step of forming an implant mask in the center part ofthe first main surface and then implanting the silicon ions from theside of the edge part and from the side of the first main surface of theSOI substrate.

A fourth aspect of the present invention is directed to a method forprocessing a semiconductor substrate having a first main surface, asecond main surface on the opposite side, and a side part, wherein apart where an active region is formed in the first main surface isdefined as a center part, and a part including a peripheral regionaround the center part in the first main surface and the side part isdefined as an edge part. According to the fourth aspect, thesemiconductor substrate processing method comprises the steps of (a)forming an insulating film to cover the edge part of the semiconductorsubstrate, (b) implanting oxygen ions from the side of the first mainsurface of the semiconductor substrate comprising the insulating film toform a buried oxide film and an SOI layer in a sequentially stacked formin the first main surface by an SIMOX method, and (c) removing theinsulating film, thereby forming an SOI substrate having the buriedoxide film extending in parallel with the main surface to the outermostend of the edge part.

Preferably, according to a fifth aspect of the present invention, in thesemiconductor substrate processing method, the insulating film is formedto a thickness, in its thickest part, equal to or larger than a totalthickness of the buried oxide film and the SOI layer, and the step (a)comprises the step of forming a thermal oxide film by a thermaloxidation method as the insulating film.

Preferably, according to a sixth aspect of the present invention, in thesemiconductor substrate processing method, the insulating film is formedto a thickness, in its thickest part, equal to or larger than a totalthickness of the buried oxide film and the SOI layer, and the step (a)comprises the step of forming a TEOS film by a low pressure CVD methodas the insulating film.

A seventh aspect of the present invention is directed to a method forprocessing a semiconductor substrate having a first main surface, asecond main surface on the opposite side, and a side part, wherein apart where an active region is formed in the first main surface isdefined as a center part, and a part including a peripheral regionaround the center part in the first main surface and the side part isdefined as an edge part. According to the seventh aspect of the presentinvention, the semiconductor substrate processing method comprises thesteps of (a) applying a first oxygen-ion implantation from the side ofthe first main surface of the semiconductor substrate all over thesurface, (b) selectively applying a second oxygen-ion implantation intothe edge part from the side of the first main surface of thesemiconductor substrate, and (c) applying an annealing processing todiffuse the oxygen ions implanted by the first and second oxygen-ionimplantations to form a buried oxide film and a protective oxide filmrespectively in the center part and in the edge part and also to form anSOI layer on the buried oxide film, wherein the second oxygen-ionimplantation has its implant peak set at a shallower position than thatin the first oxygen-ion implantation, and the protective oxide film isformed in the edge part on at least the side of the first main surfacefrom the surface to the inside.

Preferably, according to an eighth aspect of the present invention, inthe semiconductor substrate processing method, the step (c) comprisesthe steps of applying a first annealing processing prior to the step (b)to form the buried oxide film and the SOI layer, and applying a secondannealing processing after the step (b) to form the protective oxidefilm.

According to a ninth aspect of the present invention, a semiconductorsubstrate processing method comprises the steps of: (a) forming by abonding method a stacked structure comprising a first semiconductorsubstrate, an on-substrate oxide film, and a second semiconductorsubstrate having an outside dimension larger than that of theon-substrate oxide film, the on-substrate oxide film and the secondsemiconductor substrate being sequentially stacked on a main surface ofthe first semiconductor substrate, (b) pressing down the secondsemiconductor substrate from above to bring a main surface of the secondsemiconductor substrate protruding over the main surface of the firstsemiconductor substrate into contact with the main surface of the firstsemiconductor substrate and bonding the first and second semiconductorsubstrates by a bonding method; and (c) polishing the secondsemiconductor substrate to a predetermined thickness to form an SOIlayer.

A tenth aspect of the present invention is directed to a semiconductorsubstrate having a first main surface, a second main surface on theopposite side, and a side part, wherein a part where an active region isformed in the first main surface is defined as a center part, and a partincluding a peripheral region around the center part in the first mainsurface and the side part is defined as an edge part. According to thetenth aspect, the semiconductor substrate comprises: a buried oxide filmand an SOI layer formed in the first main surface in a sequentiallystacked form; a doped polysilicon layer formed in the edge part to coverthe edge part; and a protective oxide film formed in said dopedpolysilicon layer on at least the side of the first main surface fromthe surface to the inside.

Preferably, according to an eleventh aspect of the present invention, inthe semiconductor substrate, a thickness of the doped polysilicon layerin its thickest part in the edge part is equal to or larger than a totalthickness of the buried oxide film and the SOI layer, and the dopedpolysilicon layer is formed also on the second main surface.

The present invention includes a method for processing a semiconductorsubstrate having one main surface, the other main surface on theopposite side, and a side part, wherein a part where an active region isformed in the one main surface is defined as a center part, and a partincluding a peripheral region around the center part in the one mainsurface and the side part is defined as an edge part, the semiconductorsubstrate processing method comprising the steps of: (a) forming a dopedpolysilicon layer to cover the edge part of the semiconductor substrate;and (b) implanting oxygen ions from the side of the one main surface ofthe semiconductor substrate having the doped polysilicon layer to form aburied oxide film and an SOI layer in a sequentially stacked form in theone main surface by an SIMOX method and also to form a protective oxidefilm in the doped polysilicon layer on at least the side of the one mainsurface from the surface to the inside.

The present invention is directed to the semiconductor substrateprocessing method, wherein the doped polysilicon layer is formed to athickness, in its thickest part in the edge part, equal to or largerthan a total thickness of the buried oxide film and the SOI layer, andwherein the step (a) comprises the step of forming the doped polysiliconlayer also on the other main surface of the semiconductor substrate.

The present invention includes a method for processing a semiconductorsubstrate having one main surface, the other main surface on theopposite side, and a side part, wherein a part where an active region isformed in the one main surface is defined as a center part, and a partincluding a peripheral region around the center part in the one mainsurface and the side part is defined as an edge part, wherein thesemiconductor substrate is an SOI substrate formed by an SIMOX method,and the semiconductor substrate comprises a buried oxide film and an SOIlayer sequentially stacked in the one main surface, and wherein a laserbeam is applied to the edge part from above in a vacuum to mix the SOIlayer and the buried oxide film to form a molten layer in the edge parton the side of the one main surface at least.

The present invention includes a method for processing a semiconductorsubstrate having an on-substrate oxide film and an SOI layersequentially stacked on one main surface of the semiconductor substrate,comprising the step of applying a laser beam from above to an edge partof the on-substrate oxide film and the SOI layer in a vacuum to mix theSOI layer and the on-substrate oxide film to form a molten layer in theedge part.

The present invention includes a semiconductor substrate having one mainsurface, the other main surface on the opposite side, and a side part,wherein a part where an active region is formed in the one main surfaceis defined as a center part, and a part including a peripheral regionaround the center part in the one main surface and the side part isdefined as an edge part, the semiconductor substrate comprising, aburied oxide film and an SOI layer formed in the one main surface in asequentially stacked form, and a protective oxide film formed in theedge part on at least the side of the one main surface from the surfaceto the inside.

The present invention includes semiconductor substrate having one mainsurface, the other main surface on the opposite side, and a side part,wherein a part where an active region is formed in the one main surfaceis defined as a center part, and a part including a peripheral regionaround the center part in the one main surface and the side part isdefined as an edge part, the semiconductor substrate comprising, aburied oxide film and an SOI layer formed in the one main surface in asequentially stacked form, and a molten layer formed by mixing the SOIlayer and the buried oxide film in the edge part on the side of the onemain surface at least.

The present invention includes a semiconductor substrate comprising anon-substrate oxide film and an SOI layer sequentially stacked on onemain surface of the semiconductor substrate, which comprises a moltenlayer formed by mixing the SOI layer and the on-substrate oxide film inat least an edge part of the on-substrate oxide film and the SOI layerto cover the edge part.

The present invention includes a semiconductor substrate comprising anon-substrate oxide film and an SOI layer sequentially stacked on onemain surface of the semiconductor substrate, which comprises anepitaxial layer formed on at least an edge part of the on-substrateoxide film and the SOI layer to cover the edge part.

According to the semiconductor substrate processing method of the firstaspect of the present invention, the buried oxide film disappears in theedge part. In the process of thinning the SOI layer, for example, thisprevents the problem that the SOI layer in the edge part is partiallysurrounded by the buried oxide film and an oxide film formed for thethinning process, partially lifted off in removal of the oxide film tobe particles, and suspended in etching solution. This prevents defectiveformation of semiconductor elements due to the presence of particles,leading to improved production yield.

According to the semiconductor substrate processing method of the secondaspect of the present invention, it is possible to eliminate the buriedoxide film formed in the edge part only by an ion implantation from asingle direction. This method is efficient and suppresses an increase inproduction cost due to the application of the invention.

According to the semiconductor substrate processing method of the thirdaspect of the present invention, it is possible to eliminate the buriedoxide film not only in the edge part but also in a desired region in thecenter part. This allows the buried oxide film to be absent in a largeregion.

According to the semiconductor substrate processing method of the fourthaspect of the present invention, the buried oxide film extends to theoutermost end of the edge in parallel with the main surface. Hence, athin SOI layer is not formed on the buried oxide film in the edge part.In the process of thinning the SOI layer, for example, this prevents theproblem that a thin SOI layer 1 is partially surrounded by the buriedoxide film and an oxide film formed for the thinning process, partiallylifted off in removal of the oxide film to be particles, and suspendedin etching solution. This prevents defective formation of semiconductorelements due to the presence of particles, leading to improvedproduction yield.

According to the semiconductor substrate processing method of the fifthaspect of the present invention, the thickness of the thickest part ofthe insulating film is set to be equal to or larger than the totalthickness of the buried oxide film and the SOI layer so that the curvedpart of the buried oxide film is formed inside the insulating film. Thisprevents formation of the curved part of the buried oxide film in theedge part of the semiconductor substrate. Further, since the insulatingfilm is formed as a thermal oxide film, it can easily be obtained with asuppressed increase in production cost due to the application of theinvention.

According to the semiconductor substrate processing method of the sixthaspect of the present invention, the thickness of the thickest part ofthe insulating film is set to be equal to or larger than the totalthickness of the buried oxide film and the SOI layer so that the curvedpart of the buried oxide film is formed inside the insulating film. Thisprevents formation of the curved part of the buried oxide film in theedge part of the semiconductor substrate. Further, the insulating filmis formed as a TEOS film, a good insulating film having less pinholes.

According to the semiconductor substrate processing method of seventhaspect of the present invention, a protective oxide film is formed inthe edge part on, at least, the first main surface side from the surfaceto the inside. This prevents formation of a thin SOI layer on the buriedoxide film in the edge part. In the process of thinning the SOI layer,for example, this prevents the problem that a thin SOI layer ispartially surrounded by the buried oxide film and an oxide film formedfor the thinning process, partially lifted off in removal of the oxidefilm to be particles, and suspended in etching solution. This in turnprevents defective formation of semiconductor elements due to thepresence of particles, leading to improved production yield. Further,the protective oxide film is formed by using an ion implantation methodand grown by annealing, as well as the buried oxide film. Therefore noextra devices nor extra process steps are required for the formation ofthe protective oxide film, suppressing an increase in production costdue to the application of the present invention.

According to the semiconductor substrate processing method of the eighthaspect of the present invention, the formation of the buried oxide filmand the formation of the protective oxide film are accomplished byseparate annealing processes, which provides good controllability forthickness of the individual oxide films.

The semiconductor substrate processing method of the ninth aspect of thepresent invention provides a semiconductor substrate formed by a bondingmethod, which has an on-substrate oxide film covered by an SOI layer. Inwet etching for thinning the SOI layer, for example, this prevents theproblem that the on-substrate oxide film is partially removed and theSOI layer thereon is put in a partially hanging state, therebypreventing exfoliation of the SOI layer and hence formation ofparticles.

According to the semiconductor substrate of the tenth aspect of thepresent invention, the doped polysilicon layer is composed of aprotective oxide film in the edge part on the first main surface side atleast, so that a thin SOI layer is not formed on the buried oxide filmin the edge part. In the process of thinning the SOI layer, for example,this prevents the problem that a thin SOI layer is partially surroundedby the buried oxide film and an oxide film formed for the thinningprocess, partially lifted off in removal of the oxide film to beparticles, and suspended in etching solution.

The semiconductor substrate of the eleventh aspect of the presentinvention provides a specific structure for forming the dopedpolysilicon layer with a protective oxide film in the edge part on thefirst main surface side at least. Further, the doped polysilicon layeris formed also on the second main surface, which can be used as agettering layer.

The present invention has been made to solve the problems describedabove, and an object of the present invention is to provide asemiconductor substrate processing method and a semiconductor substratethat can prevent formation of particles from the edge part of thesubstrate.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view used to describe a semiconductorsubstrate processing process according to a first preferred embodimentof the present invention.

FIG. 2 is a cross-sectional view used to describe the structure of thesemiconductor substrate according to the first preferred embodiment ofthe present invention.

FIG. 3 is a cross-sectional view used to describe the semiconductorsubstrate processing process according to the first preferred embodimentof the present invention.

FIG. 4 is a cross-sectional view used to describe a modification of thesemiconductor substrate processing process according to the firstpreferred embodiment of the present invention.

FIGS. 5 and 6 are cross-sectional views used to describe a semiconductorsubstrate processing process according to a second preferred embodimentof the present invention.

FIG. 7 is a cross-sectional view used to describe the structure of thesemiconductor substrate according to the second preferred embodiment ofthe present invention.

FIG. 8 is a cross-sectional view used to describe a structure of asemiconductor substrate according to the second preferred embodiment ofthe present invention.

FIG. 9 is a cross-sectional view used to describe the structure of amodification of the semiconductor substrate according to the secondpreferred embodiment of the present invention.

FIG. 10 is a cross-sectional view used to describe a modification of thesemiconductor substrate processing process according to the secondpreferred embodiment of the present invention.

FIGS. 11 and 12 are cross-sectional views used to describe asemiconductor substrate processing process according to a thirdpreferred embodiment of the present invention.

FIG. 13 is a cross-sectional view used to describe the structure of thesemiconductor substrate according to the third preferred embodiment ofthe present invention.

FIG. 14 is a cross-sectional view used to describe a semiconductorsubstrate processing process according to a fourth preferred embodimentof the present invention.

FIG. 15 is a cross-sectional view used to describe the structure of thesemiconductor substrate according to the fourth preferred embodiment ofthe present invention.

FIG. 16 is a cross-sectional view used to describe a structure of asemiconductor substrate according to the fourth preferred embodiment ofthe present invention.

FIG. 17 is a cross-sectional view used to describe a semiconductorsubstrate processing process according to a fifth preferred embodimentof the present invention.

FIG. 18 is a cross-sectional view used to describe the structure of thesemiconductor substrate according to the fifth preferred embodiment ofthe present invention.

FIG. 19 is a plane view used to describe the semiconductor substrateprocessing process according to the fifth preferred embodiment of thepresent invention.

FIG. 20 is a cross-sectional view used to describe a semiconductorsubstrate processing process according to a sixth preferred embodimentof the present invention.

FIG. 21 is a cross-sectional view used to describe the structure of thesemiconductor substrate according to the sixth preferred embodiment ofthe present invention.

FIG. 22 is a cross-sectional view used to describe a semiconductorsubstrate processing process according to a seventh preferred embodimentof the present invention.

FIG. 23 is a cross-sectional view used to describe the structure of thesemiconductor substrate according to the seventh preferred embodiment ofthe present invention.

FIGS. 24 to 26 are cross-sectional views used to describe asemiconductor substrate processing process according to an eighthpreferred embodiment of the present invention.

FIG. 27 is a cross-sectional view used to describe the structure of thesemiconductor substrate according to the eighth preferred embodiment ofthe present invention.

FIG. 28 is a cross-sectional view used to describe a semiconductorsubstrate processing process according to a ninth preferred embodimentof the present invention.

FIG. 29 is a cross-sectional view used to describe the structure of thesemiconductor substrate according to the ninth preferred embodiment ofthe present invention.

FIG. 30 is a cross-sectional view used to describe a modification of thesemiconductor substrate processing process according to the ninthpreferred embodiment of the present invention.

FIG. 31 is a cross-sectional view used to describe the structure of themodification of the semiconductor substrate according to the ninthpreferred embodiment of the present invention.

FIG. 32 is a cross-sectional view used to describe the structure of anSOI structure formed on a semiconductor substrate formed by a CZ method.

FIG. 33 is a cross-sectional view used to describe the structure of theedge part of the SOI substrate.

FIGS. 34 and 35 are cross-sectional views used to describe a problem ina conventional SOI substrate processing method.

FIGS. 36 and 37 are cross-sectional views used to describe a problem ofan SOI substrate formed by a bonding method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A. First Preferred Embodiment

A semiconductor substrate processing method and a semiconductorsubstrate according to a first preferred embodiment of the presentinvention will now be described referring to FIG. 1 to FIG. 4. In thefollowing description, a semiconductor substrate is referred toseparately in its upper main surface (the side on which semiconductorelements are formed), center part thereof (including the active regionin which semiconductor elements are actually formed), edge partincluding the peripheral part around the center part and the side, andlower main surface.

<A-1. Processing Method>

FIG. 1 is a diagram showing a partial section of an SOI substrate 10formed by an SIMOX (Separation by Implanted Oxygen) method. In the SIMOXmethod, an SOI structure is obtained by implanting oxygen ions to dosesof 1×10¹⁸ to 2×10¹⁸/cm² at 150 to 200 KeV and then annealing it at about1300 to 1400° C. The SOI substrate 10 includes a buried oxide film 2 anda single-crystal silicon layer (hereinafter referred to as an SOI layer)1 sequentially stacked in the upper main surface of a single-crystalsilicon substrate 3. The thickness of the buried oxide film 2 is about0.05 to 0.5 μm, and the thickness of the SOI layer 1 is about 0.05 to0.3 μm.

As shown in FIG. 1, the edge part forms a curved surface with largecurvature. Accordingly, when oxygen ions are implanted from the verticaldirection into the main surface to form the buried oxide film 2, theoxygen ions are obliquely implanted into the edge part, so that theeffective implantation energy is reduced. As a result, the buried oxidefilm 2 and the SOI layer 1 are thinner in the edge part. The surface ofthe edge part is not smooth but rough with irregularities.

Silicon (Si) ions are implanted into the edge part of the SOI substrate10. The silicon ions are implanted in the direction of radiuses of theSOI substrate 10 under the conditions of doses of 1×10¹⁵ to 5×10¹⁵/cm²and energies of 300 to 400 KeV, to a depth of about 1 μm from thesubstrate surface.

When silicon ions are to be implanted only into the edge part, implantmask may be formed on the upper and lower main surfaces of the SOIsubstrate 10. In ion implantation, implanting ions with the SOIsubstrate 10 rotated around the center allows the ions to be implantedinto the entirety of the periphery of the SOI substrate 10.

As a result, the buried oxide film 2 in the edge part of the SOIsubstrate 10 becomes rich with silicon, and then the buried oxide film 2substantially disappears in the SOI substrate 100, as shown in FIG. 2.

The buried oxide film 2 is eliminated in the region about 1 μm deep fromthe edge surface of the SOI substrate 10, resulting in the absence ofthe buried oxide film 2 exposed from the SOI substrate 10.

<A-2. Characteristic Functions and Effects>

The above-described first preferred embodiment of the present inventionsolves the problem that in a process of thinning the SOI layer 1, forexample, the SOI layer 1 in the edge part is partially surrounded by theburied oxide film 2 and an oxide film formed for the thinning process,partially lifted off in removal of that oxide film to be particles, andsuspended in the etching solution. This prevents defective formation ofsemiconductor elements due to the presence of particles, leading toimproved yield in manufacturing.

Needless to say, this preferred embodiment is also effective with astructure in which a polysilicon layer is formed on the edge part andthe lower main surface of the silicon substrate 3 for gettering ofcontaminants such as heavy metals.

<A-3. First Modification>

Although the description above has shown an example in which an ionimplantation is applied to a single piece of SOI substrate 10, aplurality of SOI substrates 10 may be stacked and processed in a singleion implantation process.

That is to say, as shown in FIG. 3, a plurality of SOI substrates 10 aresequentially laid on top of each other and silicon ions are implantedfrom the edge side with implant masks MS formed in the center parts ofthe main surfaces of the SOI substrates 10 on the top and bottom.

This method improves manufacturing efficiency of the SOI substrates 100.Further, this method does not require the formation of implant mask MSon the SOI substrates 10 other than the top and bottom SOI substrates10, thus reducing the production cost.

Moreover, an ion beam generally has a dimension much larger than thethickness of the SOI substrate 10. Accordingly, applying the ion beam toa plurality of SOI substrates 10 is more efficient than applying it to asingle piece of SOI substrate 10.

<A-4. Second Modification>

Although the description above has shown an example in which an ion beamis implanted from the direction of the radiuses of the SOI substrate 10,it may be implanted not only from the radial direction but also from thedirection of the upper main surface.

That is to say, as shown in FIG. 4, silicon ions are implanted from theradial direction and the upper main surface direction with implant masksformed in the part of the upper main surface of the SOI substrate 10where silicon ions are not to be implanted.

This method eliminates the buried oxide film 2 not only in the edge partof the SOI substrate 10 but also over a desired region in the centerpart. For example, it is possible to remove the buried oxide film 2 in aregion about 1 mm inside the outermost part of the edge.

The buried oxide film 2 can be eliminated when the implant depth ofsilicon ions is deeper than the total of the thickness of the buriedoxide film 2 (about 0.05 to 0.5 μm) and the thickness of the SOI layer 1(about 0.05 to 0.3 μm).

Accordingly, this method is effective when the buried oxide film 2cannot be eliminated over a desired region only by implanting siliconions from the radial direction of the SOI substrate 10.

B. Second Preferred Embodiment

A semiconductor substrate processing method and a semiconductorsubstrate according to a second preferred embodiment of the presentinvention will now be described referring to FIG. 5 to FIG. 10.

<B-1. Processing Method>

First, as shown in FIG. 5, an oxide film 8 is formed in the edge part ofa silicon substrate 3 formed by a CZ (Czochralski) method. In FIG. 5,the oxide film 8 is formed to cover the edge part of the siliconsubstrate 3. Formed in the center part of the upper and lower mainsurfaces of the silicon substrate 3 are oxidation preventing masks MS1,where the oxide film 8 is not formed.

The oxide film 8 is formed with its largest thickness equal to or largerthan the total thickness of the buried oxide film and the SOI layer thatwill be formed in the silicon substrate 3 later. Since the buried oxidefilm is about 0.05 to 0.5 μm thick and the SOI layer 1 is about 0.05 to0.3 μm thick, the thickness of the thickest part of the oxide film 8 isabout 0.1 to 0.8 μm. The oxide film 8 is formed by a thermal oxidationmethod under temperature condition of about 900 to 1200° C.

Next, after removing the oxidation preventing masks MS1, oxygen ions areimplanted from the upper main surface side of the silicon substrate 3 asshown in FIG. 6 to form a buried oxide film 2 inside the siliconsubstrate 3 and inside the oxide film 8 by SIMOX method. The oxygen ionimplantation and the following annealing are performed under the sameconditions as those in the first preferred embodiment, which are notdescribed here again.

The buried oxide film 2 and the oxide film 8 cannot be clearlydistinguished in the oxide film 8. The buried oxide film 2 is formedmerely as a somewhat oxygen-richer region by the oxygen ionimplantation. However, the buried oxide film 2 is shown by broken linesin FIG. 6 to clearly show the structure.

Finally, the oxide film 8 is removed by wet etching by using etchingsolution, e.g., an HF solution, to obtain an SOI substrate 200 havingthe buried oxide film 2 extending to the outermost edge in parallel withthe main surface, as shown in FIG. 7.

<B-2. Characteristic Functions and Effects>

According to the above-described second preferred embodiment of thepresent invention, the buried oxide film 2 is formed to the outermostpart of the edge in parallel with the main surface, without a thin SOIlayer 1 formed on the buried oxide film 2. This solves the problem that,in the process of thinning the SOI layer 1, for example, a thin SOIlayer 1 is partially surrounded by the buried oxide film 2 and an oxidefilm formed for the thinning process, partially lifted off in removal ofthe oxide film to be particles, and suspended in the etching solution.This prevents defective formation of semiconductor elements due to thepresence of particles, leading to improved production yield.

Further, in the edge part, of the SOI substrate 200 shown in FIG. 7, thesurface condition is improved, without irregularities. The finalcondition of the edge surface of the SOI substrate 200 is smooth becausethe surface of the silicon substrate 3 is oxidized to become the oxidefilm 8 in the formation of the oxide film 8 in the edge part of thesilicon substrate 3 and then the oxide film 8 is removed.

Needless to say, this preferred embodiment is also effective with astructure in which a polysilicon layer is formed on the edge part andthe lower main surface of the silicon substrate 3 for gettering ofcontaminants such as heavy metals. FIG. 8 shows an SOI substrate 200Ahaving a polysilicon layer 4 for gettering.

The polysilicon layer 4 is formed on the edge part and the lower mainsurface of the silicon substrate 3 prior to the formation of the SOIstructure and the oxide film 8 is formed from above the polysiliconlayer 4. Accordingly, although the thickness of the polysilicon layer 4is somewhat reduced in the formation of the oxide film 8, thepolysilicon layer 4 remains after the oxide film 8 has been removedafter the formation of the SOI structure. The SOI substrate 200A shownin FIG. 8 is thus obtained.

<B-3. Modification>

The description above has shown an example in which the oxide film 8 isformed by a thermal oxidation method in the edge part of the siliconsubstrate 3. However, an oxide film 9 may be formed with TEOS(tetraethylorthosilicate) as shown in FIG. 9 (hereinafter referred to asa TEOS film).

FIG. 9 corresponds to FIG. 6. This diagram shows the process of formingthe TEOS film 9 in the edge part of the silicon substrate 3 and thenimplanting oxygen ions from the upper main surface side of the siliconsubstrate 3 to form the buried oxide film 2 inside the silicon substrate3 and inside the TEOS film 9 by

As shown in FIG. 9, although the buried oxide film 2 is curved in theTEOS film 9, it extends in parallel with the main surface in the siliconsubstrate 3. Accordingly, when the TEOS film 9 is removed, the samestructure as the SOI substrate 200A shown in FIG. 7 is obtained.

The TEOS film 9 is an oxide film formed by a low-pressure CVD method byusing TEOS under temperature condition of 650 to 750° C., which is agood oxide film with less pinholes.

In the formation of the TEOS film 9, when a plurality of siliconsubstrates 3 are put in low-pressure CVD equipment in a stacked form asshown in FIG. 10, the oxidation preventing masks MS1 can be formed onlyon the main surfaces of the top and bottom silicon substrates 3. Ascompared with a case in which the oxidation preventing masks MS1 areformed on each single piece, this improves the manufacturing efficiency.

The same functions and effects can be obtained by forming a nitride filmin place of the TEOS film 9. That is to say, any insulating film can beused if it can extend the edge of the silicon substrate 3 so that thecurved portion of the buried oxide film 2 can substantially be containedtherein, preventing the formation of the curved portion of the buriedoxide film 2 in the edge part of the silicon substrate 3.

C. Third Preferred Embodiment

A semiconductor substrate processing method and a semiconductorsubstrate according to a third preferred embodiment of the presentinvention will now be described referring to FIG. 11 to FIG. 13.

<C-1. Processing Method>

First, as shown in FIG. 11, a doped polysilicon layer 11 is formed inthe edge part and the lower main surface of a silicon substrate 3 formedby the CZ method. In FIG. 11, a mask MS2 for preventing the formation ofpolysilicon is formed in the center part of the upper main surface ofthe silicon substrate 3, where the doped polysilicon layer 11 is notformed. The doped polysilicon layer 11 is formed with its largestthickness equal to or larger than the total thickness of the buriedoxide film and the SOI layer that will be formed in the siliconsubstrate 3 later. The buried oxide film is about 0.05 to 0.5 μm thickand the SOI layer 1 is about 0.05 to 0.3 μm thick, so that the thicknessof the thickest part of the doped polysilicon layer 11 is about 0.1 to0.8 μm.

The doped polysilicon layer 11 can be formed by in-situ doping by usinga gas that contains impurities, e.g., phosphorus or boron, together witha material gas for the polysilicon layer to introduce impuritiessimultaneously with the formation of the polysilicon layer by a CVDmethod.

Next, after removal of the polysilicon formation preventing mask MS2, anoxygen ion implantation is applied from the upper main surface side ofthe silicon substrate 3 as shown in FIG. 12 to form an oxygen-implantedregion 2A inside the silicon substrate 3 and inside the dopedpolysilicon layer 11 by an SIMOX method. FIG. 12 shows the structurebefore annealing.

Next, the silicon substrate 3 containing the oxygen-implanted region 2Ais annealed to diffuse oxygen in the oxygen-implanted region 2A toexpand the oxidized region for formation of the buried oxide film 2 andto recover the crystallinity of the silicon substrate 3 for formation ofthe SOI layer 1. At this time, oxidation rapidly progresses in the dopedpolysilicon layer 11, because of the difference between the oxidizingrate of the doped polysilicon layer 11 and the oxidizing rate of thesilicon substrate 3, to provide an SOI substrate 300 having a thickoxide film 12 (protective oxide film) reaching the surface of the edgepart of the doped polysilicon layer 11 as shown in FIG. 13. Theoxidizing rates of doped polysilicon and single-crystal silicon are in aratio of about 2 to 1. The oxygen ion implant and the annealing afterthe implant are applied under the same conditions as those described inthe first preferred embodiment, and therefore they are not describedhere again.

<C-2. Characteristic Functions and Effects>

According to the above-described third preferred embodiment of thepresent invention, as shown in FIG. 13, the doped polysilicon layer 11is composed of the oxide film 12 in the edge part on the upper mainsurface side at least, without a thin SOI layer 1 formed on the buriedoxide film 2. This prevents the problem that, in the process of thinningthe SOI layer 1, for example, a thin SOI layer 1 is partially surroundedby the buried oxide film 2 and an oxide film formed for the thinningprocess, partially lifted off to form particles in removal of the oxidefilm, and suspended in etching solution. This prevents defectiveformation of semiconductor elements due to the presence of particles,leading to improvement of the production yield.

In the edge part of the SOI substrate 300 shown in FIG. 13, the surfacecondition of the silicon substrate 3 is improved, with noirregularities. This is because the surface of the silicon substrate 3is oxidized to become the oxide film 12 in oxidization of the dopedpolysilicon layer 11.

The doped polysilicon layer 11 may be left in the edge part and thelower main surface of the silicon substrate 3 to be used as a getteringlayer for gettering of contaminants like heavy metals in the siliconsubstrate 3.

D. Fourth Preferred Embodiment

A semiconductor substrate processing method and a semiconductorsubstrate according to a fourth preferred embodiment of the presentinvention will now be described referring to FIG. 14 to FIG. 16.

<D-1. Processing Method>

First, an oxygen ion implantation (a first implantation) is applied fromthe upper main surface side of a silicon substrate 3 formed by a CZmethod to form a first oxygen-implanted region. Then annealing isapplied to form a buried oxide film 2 inside the silicon substrate 3.The oxygen ion implantation and the following annealing are performedunder the same conditions as the first preferred embodiment, which arenot described here again.

After that, as shown in FIG. 14, an implant mask MS is formed in thecenter part of the upper main surface of the silicon substrate 3 and anoxygen ion implantation (a second implantation) is applied from theupper main surface side of the silicon substrate 3 to form anoxygen-implanted region on the buried oxide film 2 in the edge part. Theoxygen ion implantation is performed under the conditions of an energyof about 50 KeV and doses of 1×10¹⁸ to 2×10¹⁸/cm².

After that, annealing is applied to facilitate oxidation to form anoxide film 13 (protective oxide film) that reaches the surface of thesilicon substrate 3 above the buried oxide film 2 in the edge part. TheSOI substrate 400 shown in FIG. 15 is thus obtained.

The processes of annealing for the formation of the buried oxide film 2and for the formation of the oxide film 13 are performed under almostthe same conditions. Therefore the buried oxide film 2 and the oxidefilm 13 may be formed at the same time by applying an annealing processafter the first and second oxygen ion implantation processes.

<D-2. Characteristic Functions and Effects>

According to the above-described fourth preferred embodiment of thepresent invention, as shown in FIG. 15, the edge part on the upper mainsurface side of the SOI substrate 400 is formed of the oxide film 13,without a thin SOI layer 1 formed on the buried oxide film 2.Accordingly, for example, in the process of thinning the SOI layer 1,this prevents the problem that a thin SOI layer 1 is partiallysurrounded by the buried oxide film 2 and an oxide film formed forthinning, partially lifted off in removal of the oxide film to formparticles, and suspended in the etching solution. This preventsdefective formation of semiconductor elements due to the presence ofparticles, leading to improved production yield.

Similarly to the buried oxide film 2, the oxide film 13 can be formed byusing an ion implantation method and grown by annealing. It is thereforenot necessary to use extra devices or to add extra process steps for theformation of the oxide film 13, which suppresses an increase inproduction cost.

When the buried oxide film 2 and the oxide film 13 are annealed inseparate process steps, these oxide films can be treated with goodcontrollability for thickness.

Needless to say, this preferred embodiment is effective also with astructure in which a polysilicon layer is formed on the edge part andthe lower main surface of the silicon substrate 3 for gettering ofcontaminants such as heavy metals. FIG. 16 shows an SOI substrate 400Ahaving a polysilicon layer 4 for gettering.

E. Fifth Preferred Embodiment

A semiconductor substrate processing method and a semiconductorsubstrate according to a fifth preferred embodiment of the presentinvention will now be described referring to FIG. 17 to FIG. 19.

<E-1. Processing Method>

First, oxygen ions are implanted (a first implantation) into a siliconsubstrate 3 formed by the CZ method from the upper main surface side toform a buried oxide film 2 inside the silicon substrate 3 by the SIMOXmethod. The oxygen ion implantation and annealing after the implantationare performed under the same conditions as those in the first preferredembodiment, which are not described here again.

After that, as shown in FIG. 17, a laser beam LB is applied from aboveto the edge part of the silicon substrate 3 in a vacuum. An Nd-YAG laser(with a wavelength 1.06 μm) is used as the laser source, with a laseroutput of about 3 to 5 W (watts), for example. The spot size of thelaser beam LB is about 2 to 3 μm.

The application of the laser beam LB under the above-describedconditions melts the irradiated part, so that the SOI layer 1 and theburied oxide film 2 are mixed together. Then, as shown in FIG. 18, anSOI substrate 500 having a molten layer 14 in the edge part on, atleast, the upper main surface side of the substrate is obtained.

As for the composition of the molten layer 14, it is known that theoxide film is at least silicon-richer than SiO₂. However, the phenomenonthat silicon and silicon oxide are melted with a laser beam falls withinan unknown field. Since neither the inventors nor others have found thecomposition of the molten layer 14 in research, the composition of themolten layer 14 is assumed to be SiO_(x).

To apply the laser beam LB uniformly all over to the edge part of thesilicon substrate 3, the silicon substrate 3 is rotated in the directionshown by the arrow A with the laser beam LB fixed in a position in theedge part as shown in FIG. 19, for example. After the silicon substrate3 has been rotated once, the laser beam LB is moved in the directionshown by the arrow B or C and fixed there, and the silicon substrate 3is turned again. Repeating this operation allows the laser beam LB to beapplied uniformly all over in the edge part of the silicon substrate 3.

Although the number of revolutions of the silicon substrate 3 and theirradiation time for each point depend on the intensity and spot size ofthe laser beam LB, it is known that the silicon substrate 3 can bemelted almost in an instant with the above-described specification ofthe laser beam LB.

<E-2. Characteristic Functions and Effects>

According to the above-described fifth preferred embodiment of thepresent invention, as shown in FIG. 18, the edge part of the upper mainsurface side of the SOI substrate 500 is composed of the molten layer14, which eliminates the irregularities on the edge part of the siliconsubstrate 3 and also eliminates the presence of a thin SOI layer 1 onthe buried oxide film 2. This solves the problem that, in the process ofthinning the SOI layer 1, for example, a thin SOI layer 1 is partiallysurrounded by the buried oxide film 2 and an oxide film formed forthinning, partially lifted off in removal of the oxide film to beparticles, and suspended in the etching solution. This preventsdefective formation of semiconductor elements due to the presence ofparticles, leading to improvement of the production yield.

Although marking with a laser beam to a silicon substrate (marking fordiscrimination of silicon substrates) is generally known, it isrecognized merely as a marking method. Generally, the composition of themarked part has not been sufficiently studied. As a matter of course,there has never been the technical idea of preventing formation ofparticles from SOI substrates by using a laser beam.

The inventors and others have paid attention to the phenomenon thatsilicon evaporates and melts in a silicon substrate marking process witha laser beam and found that the application of a laser beam to atwo-layer structure of a silicon layer and a silicon oxide film causesthe silicon layer and the silicon oxide film to be mixed to form anoxide film silicon-richer than an ordinary silicon oxide film. On thebasis of this finding, we have reached the technical idea of preventingformation of particles with SOI substrates by using a silicon-rich oxidefilm obtained by melting.

Although this preferred embodiment has shown an example in which a laserbeam is applied to an SOI substrate to melt the buried oxide film 2 andthe SOI layer 1, a silicon-richer oxide film can be obtained by meltingany two-layer structure of a silicon layer and a silicon oxide film withan application of a laser beam. For example, needless to say, asilicon-richer oxide film can be obtained also with a structure in whicha silicon oxide film is formed on a silicon layer.

The above-described first to fifth preferred embodiments have shown theinvention in terms of prevention of formation of particles with SOIsubstrates formed by the SIMOX method. In the following sixth to eighthpreferred embodiments of the present invention, the invention will bedescribed with respect to prevention of formation of particles with SOIsubstrates formed by bonding method (bonded SOI substrates).

F. Sixth Preferred Embodiment

A semiconductor substrate processing method and a semiconductorsubstrate according to a sixth preferred embodiment of the presentinvention will now be described referring to FIG. 20 and FIG. 21.

<F-1. Processing Method>

First, as shown in FIG. 20, a bonded SOI substrate 20 is prepared, whichincludes an on-substrate oxide film 6 and a silicon layer 7 sequentiallystacked on the upper main surface of a silicon substrate 3 to form anSOI structure. The SOI structure of the bonded SOI substrate 20 isobtained by forming an oxide film on the upper main surface of thesilicon substrate 3, bonding another silicon substrate thereon, and thenpolishing that silicon substrate to a desired thickness. The thicknessof the on-substrate oxide film 6 is about 0.1 to 1.0 μm and thethickness of the silicon layer 7 is about 0.1 to 0.3 μm. Theon-substrate oxide film 6 corresponds to the buried oxide film and thesilicon layer 7 corresponds to the SOI layer.

Subsequently, an epitaxial layer 15 is formed to cover the edge part ofthe upper main surface of the SOI substrate 20, the on-substrate oxidefilm 6, and the silicon layer 7. The epitaxial layer 15 is formed byexposing the SOI substrate 20 to a gas atmosphere of trichlorosilane(SiHCl₃) under temperature condition of 1150 to 1200° C., for example. Amask is formed on the lower main surface and the edge part of the lowermain surface side of the substrate where the formation of the epitaxiallayer 15 is unwanted.

Since the growth rate of the epitaxial layer 15 is 0.5 to 3.0 μm/min, ittakes about one minute to become thick enough to cover the on-substrateoxide film 6 and the silicon layer 7.

Next, as shown in FIG. 21, the epitaxial layer 15 is polished to form aflat surface above the silicon layer 7 to provide an SOI substrate 600having the epitaxial layer 15 covering the edge part of the on-substrateoxide film 6 and the silicon layer 7.

<F-2. Characteristic Functions and Effects>

According to the above-described sixth preferred embodiment of thepresent invention, as shown in FIG. 21, the edge part of theon-substrate oxide film 6 and the silicon layer 7 is covered with theepitaxial layer 15. This prevents the problem that, in wet etching forthinning the SOI layer (silicon layer 7), for example, the on-substrateoxide film 6 is partially removed to cause the silicon layer 7 thereonto be partially hung off. This prevents the silicon layer 7 from comingoff to form particles.

Even if the edge part of the on-substrate oxide film 6 and the siliconlayer 7 is imperfectly beveled and its periphery has successiveirregularities in a plane view, the irregularities are covered by theepitaxial layer 15. Hence, the on-substrate oxide film 6 and the siliconlayer 7 will not be peeled off to form particles in transportation ofthe substrate.

The description above has shown an example in which the epitaxial layer15 having good crystallinity is left on the silicon layer 7 and used asan SOI layer. However, as long as the on-substrate oxide film 6 and thesilicon layer 7 are covered, it may be removed from above the siliconlayer 7.

G. Seventh Preferred Embodiment

A semiconductor substrate processing method and a semiconductorsubstrate according to a seventh preferred embodiment of the presentinvention will now be described referring to FIG. 22 and FIG. 23.

<G-1. Processing Method>

First, a bonded SOI substrate 20 is prepared, which has an on-substrateoxide film 6 and a silicon layer 7 sequentially stacked on the uppermain surface of a silicon substrate 3 to form an SOI structure.

Subsequently, as shown in FIG. 22, a laser beam LB is applied to theedge part of the on-substrate oxide film 6 and the silicon layer 7 fromabove. An Nd-YAG laser (having a wavelength of 1.06 μm) is used as thelaser source, with a laser output of about 3 to 5 W (watts), forexample. The spot size of the laser beam LB is about 2 to 3 μm.

The application of the laser beam LB under the above-described conditioncauses the irradiated part to melt so that the silicon layer 7 and theon-substrate oxide film 6 are mixed together. Then, as shown in FIG. 23,an SOI substrate 700 is obtained with the edge part of the on-substrateoxide film 6 and the silicon layer 7 covered with a molten layer 16.

The phenomenon that the on-substrate oxide film 6 and the silicon layer7 melt is the same as the phenomenon that a silicon layer and a siliconoxide film melt as described in the fifth preferred embodiment, which isnot fully described again here.

<G-2. Characteristic Functions and Effects>

According to this preferred embodiment of the present invention, asshown in FIG. 23, the edge part of the on-substrate oxide film 6 and thesilicon layer 7 in the SOI substrate 700 is covered by the molten layer16. In the wet etching for thinning the SOI layer (silicon layer 7), forexample, this prevents the on-substrate oxide film 6 from beingpartially removed to partially put the silicon layer 7 thereon in ahanging state. This prevents the silicon layer 7 from coming off to beparticles.

Even if the edge part of the on-substrate oxide film 6 and the siliconlayer 7 is imperfectly beveled to form continuous irregularities alongthe periphery in a plane view, the irregularities are covered with themolten layer 16. This prevents the on-substrate oxide film 6 and thesilicon layer 7 from coming off to form particles in transportation ofthe substrate.

H. Eighth Preferred Embodiment

A semiconductor substrate processing method and a semiconductorsubstrate according to an eighth preferred embodiment of the presentinvention will now be described referring to FIG. 24 to FIG. 27.

<H-1. Processing Method>

First, as shown in FIG. 24, an on-substrate oxide film 61 is formed onthe upper main surface of a silicon substrate 3 and then a siliconsubstrate 31 is bonded thereon. At this time, the dimension of thesilicon substrate 31 in the plane direction is larger than that of theon-substrate oxide film 61. Accordingly, in the structure, the edge ofthe silicon substrate 31 protrudes like a visor from the edge of theon-substrate oxide film 61. The structure shown in FIG. 24 may beobtained by bonding an on-substrate oxide film 61 and a siliconsubstrate 31 having the same dimension in the plane direction and thenetching the edge part of the on-substrate oxide film 61 by a wet etchingwith HF or the like.

Next, as shown by the arrows in FIG. 25, pressures are applied to thesilicon substrate 31 from above to bend the edge part of the siliconsubstrate 31 so that part comes into contact with the surface of thesilicon substrate 3. Then, the silicon substrate 31 and the siliconsubstrate 3 are bonded together to provide the structure, as shown inFIG. 26, where the on-substrate oxide film 61 is covered with thesilicon substrate 31. The bonding is performed by using a commontechnique like a heating method, which is not described here in detail.

Finally, the silicon substrate 31 is polished to a certain thickness toform a silicon layer 7, thus providing an SOI substrate 800 in which theon-substrate oxide film 61 is covered by the silicon layer 7 as shown inFIG. 27.

<H-2. Characteristic Functions and Effects>

According to the above-described eighth preferred embodiment of thepresent invention, as shown in FIG. 27, the on-substrate oxide film 61is covered with the silicon layer 7. This prevents the problem that theon-substrate oxide film 61 is partially removed to put the silicon layer7 thereon in a partially hanging state in the wet etching for thinningthe SOI layer (silicon layer 7), for example. This prevents the siliconlayer 7 from coming off to form particles.

I. Ninth Preferred Embodiment

A semiconductor substrate processing method and a semiconductorsubstrate according to a ninth preferred embodiment of the presentinvention will now be described referring to FIG. 28 to FIG. 31.

<I-1. Processing Method>

The surface of the edge, part of a silicon substrate 3 formed by a CZmethod and having irregularities on the edge part is polished by aroller polishing as shown in FIG. 28. In the roller polishing, arotating roller having an abrasive on its cylindrical surface is broughtinto contact with an object to polish the object. In this preferredembodiment, a roller RO is brought into contact with the edge part ofthe silicon substrate 3 to polish that part.

It is desirable to polish that part into a mirror-like state, to thesame extent as the upper main surface of the silicon substrate 3, with asurface roughness of about 5 to 10 angstroms.

Next, as shown in FIG. 29, oxygen ions are implanted from the upper mainsurface side of the silicon substrate 3 to form a buried oxide film 2inside the silicon substrate 3 by the SIMOX method, to provide an SOIsubstrate 900 having a smooth edge. The oxygen ion implantation andannealing after the implantation are performed under the same conditionsas those described in the first preferred embodiment, which are notdescribed here again.

<1-2. Characteristic Functions and Effects>

According to the above-described ninth preferred embodiment of thepresent invention, the edge part of the silicon substrate 3 is broughtinto a mirror-like state and then the buried oxide film 2 is formedinside the silicon substrate 3 by SIMOX method. Accordingly, although athin SOI layer 1 is formed on the buried oxide film 2, the surfacecondition of the SOI layer 1 in that part is smooth. In the process ofthinning the SOI layer 1, for example, this prevents the problem that athin SOI layer 1 is partially surrounded by the buried oxide film 2 andan oxide film formed for thinning to be partially lifted off in removalof the oxide film and forms particles suspended in the etching solution.This prevents defective formation of semiconductor elements due to thepresence of particles, leading to improvement of the production yield.

<I-3. Modification>

Although the description above has shown an example in which the edgepart of the silicon substrate 3 is polished prior to the formation ofthe buried oxide film 2, the edge part of the silicon substrate 3 may bepolished after the buried oxide film 2 has been formed, which providesthe same effects.

More specifically, as shown in FIG. 30, a buried oxide film 2 is formedin a silicon substrate 3 having irregularities in the edge part and thenthe edge part of the silicon substrate 3 is removed by a rollerpolishing. Then, as shown in FIG. 31, an SOI substrate 900A having aburied oxide film 2 extending in parallel with the main surface to theoutermost part of the edge can be obtained. Accordingly, a thin SOIlayer 1 is not formed on the buried oxide film 2. This prevents theproblem that a thin SOI layer 1 is partially surrounded by the buriedoxide film 2 and an oxide film formed for thinning and partially liftedoff in removal of the oxide film to be particles suspended in etchingsolution. This prevents defective formation of the semiconductorelements due to the presence of the particles, leading to theimprovement of the production yield.

The above-described first to ninth preferred embodiments of the presentinvention have shown examples in which the SOI substrates haveirregularities in edge part and examples in which they have polysiliconlayers for gettering. However, the applications of the present inventionare not limited to SOI substrates. When a bulk silicon substrate havingirregularities in the edge part or a polysilicon layer for getteringsuffers from the problem of particles from the edge part, the presentinvention can be applied to prevent the formation of particles. Further,the present invention is also effective when an SOI substrate having noirregularities in the edge part suffers from the problem of theformation of particles due to the presence of thin SOI layer or buriedoxide film in the edge part.

Although it has not been described in the above first to ninth preferredembodiments of the invention, the SOI substrates obtained by theinvention are used not only for production of particular semiconductordevices. Needless to say, various semiconductor elements, such as MOStransistors and bipolar transistors, can be built in the SOI layers toproduce various semiconductor devices, such as DRAMs, SRAMs, logiccircuits, etc.

While the invention has been described in detail, the foregoingdescription is in all aspects illustrative and not restrictive. It isunderstood that numerous other modifications and variations can bedevised without departing from the scope of the invention.

1. A semiconductor substrate comprising an on-substrate oxide film andan SOI layer sequentially stacked on one main surface of saidsemiconductor substrate, which comprises a molten layer formed by mixingsaid SOI layer and said on-substrate oxide film in at least an edge partof said on-substrate oxide film and said SOI layer to cover said edgepart.
 2. A semiconductor substrate comprising an on-substrate oxide filmand an SOI layer sequentially stacked on one main surface of saidsemiconductor substrate, which comprises an epitaxial layer formed on atleast an edge part of said on-substrate oxide film and said SOI layer tocover said edge part and to overlie said SOI layer.
 3. The semiconductorsubstrate according to claim 2, wherein said epitaxial layer is formedfrom at least one of said substrate and said SOI layer.
 4. Thesemiconductor substrate according to claim 1, wherein said molten layercomprises a melted mixture of said on-substrate oxide film and said SOIlayer.